The Supreme Court of Texas eventually ruled in his favour and the airline began service in 1971.

"I knew nothing about airlines, which I think made me eminently qualified to start one," Kelleher told National Public Radio in 2016, "because what we tried to do at Southwest was get away from the traditional way that airlines had done business."

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Southwest offered cheap tickets in single-class cabins without reserved seats - tactics that became common in the airline industry several decades later.

The airline's business model, which also included shortened turnaround times at airports, cabin crew collecting rubbish, and high aircraft utilisation, has since been copied by other low-cost carriers including Ryanair of the Irish Republic and Easyjet of the UK.